Update rpc-providers.mdx

[nataly-gb]

Add GetBlock to RPC Providers

What is the purpose of the change?

Add RPC provider that supports SEI

Add new content

Describe the changes to the documentation

Add GetBlock to RPC Providers

Provide info on RPC provider that supports SEI RPC nodes

Notes

[cursor]

PR Summary

Low Risk
Documentation-only addition with no runtime or security impact.

Overview
Adds GetBlock to the RPC providers page in learn/rpc-providers.mdx as static text below the ecosystem iframe: provider name, a one-line description (“RPC node provider and infrastructure platform for Web3 and AI”), and a link to GetBlock’s Sei API docs.

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